This invention relates to a current to low pressure transducer and more particularly to a design which can provide negative output pressure or a vacuum as well as a positive output pressure.
Current to air pressure transducers are used in many industrial instrumentation and control applications. Generally these transducers provide 3-15 psig output as the input current varies over its full range. The transducer design of this invention has the capability of much lower full scale pressure change. Full scale calibrations from 1 inch of water column to 10 inches of water column can be configured. In addition the output can be set to change smoothly from a vacuum to a pressure as the input current is varied.
An important application for this transducer is with respect to air/fuel ratio control of carbureted industrial gas fueled engines. These engines are used in gas pipeline pumping stations and in many other applications. In the engine application, a fuel gas regulator is used to supply gas to the carburetor at around 5 inches of water column. The carburetor is designed to keep the air fuel ratio approximately correct as the engine load varies, but this is not precise enough for extended life of a catalytic converter and also for meeting low pollution requirements. An electronic proportional plus integral air fuel ratio controller, utilizing a zirconium oxygen sensor, can be used to obtain this needed accuracy of control. Heretofore the 3 to 15 (or 6 to 30) psig output from a current to pressure transducer has provided excursive or modulated fluid pressure to an actuator affixed to the fuel gas regulator or to a bypass valve in order to trim the air/fuel ratio. The output pressure of the current to pressure transducer of this invention can supply modulated fluid directly to the setpoint side or loading side of the fuel gas regulator and thereby save the cost and trouble of installing the cylinder or actuator.